As an example of such an electrolytic capacitor, an electrolytic capacitor has been proposed, comprising as an anode body for a capacitor a sintered body made of a valve-acting metal powder such as tantalum which can be anodized.
The electrolytic capacitor using tungsten as a valve-acting metal and employing a sintered body of the tungsten powder as an anode body can attain a larger capacitance compared to the electrolytic capacitor obtained with the same formation voltage by employing an anode body of the same volume using the tantalum powder having the same particle diameter. However, the electrolytic capacitor having the sintered body of the tungsten powder has been unpracticed as an electrolytic capacitor due to the large leakage current (LC). In order to solve this issue, a capacitor using the alloy of tungsten and other metals has been studied and has achieved some improvement in the leakage current, but it was not enough (JP-A-2004-349658; Patent Document 1).
Patent Document 2 (JP-A-2003-272959) discloses a capacitor using an electrode of a tungsten foil having formed thereon a dielectric layer selected from WO3, W2N and WN2, but the capacitor is not to solve the above-mentioned leakage current problem.
Also, Patent Document 3 (WO 2004/055843 (U.S. Pat. No. 7,154,743 B2)) discloses an electrolytic capacitor using an anode body selected from tantalum, niobium, titanium and tungsten, but it does not describe a specific example using tungsten.
As a tungsten powder which can solve the leakage current (LC) problem in the electrolytic capacitor using a sintered body of tungsten powder as an anode body, the present inventors have invented a tungsten powder, a part of the surface of which is made to be tungsten silicide so as to make the powder have a silicon content within a specific range (0.05 to 7 mass %) by mixing a tungsten powder with a silicon powder and heating the mixture under reduced pressure to thereby allow the mixture to react; an anode body for a capacitor made by sintering the powder; and an electrolytic capacitor using the anode body as an electrode, and filed a patent application (WO 2012/086272; Patent Document 4).